What's stopping you from altering the TXT record later with your own BTC address? I'll admit though it's a clever idea.
With regards to the bitcoin client, I get your point, I never thought of that, It would have to be handled by bitcoin devs themselves and if they ever wish to implement it I would be more than happy to hand the site over to them.
With regards to just remembering your BTC address, there would be no reason for me to do this to people. Most people know the first/last few letters of their bitcoin address and would surely notice any changes.
It would be good to be able to come up with an anti-tampering idea though, if anyone can think of anything.